I. Field of the Invention
This invention relates generally to lighting fixtures for residential, commercial and industrial use, and more particularly to the design of light fixtures for reducing disability glare and veiling glare without a significant loss in luminous or light output from the fixture.
II. Discussion of the Prior Art
An important aspect of light fixture design is to control glare. Light sources produce several kinds of glare. One kind of glare is discomfort or disability glare. This is due to the light source being in the field-of-view of an individual. Discomfort or disability glare can be reduced by keeping the light source out of the field-of-view. However, in many applications, this can not be done. One such application is stage and similar lighting which must be directed onto individuals. This invention can increase the size area of the source image and reduce surface luminance so that the illumination can be maintained or adjusted to desired levels. By controlled spreading of the light source, illumination can be achieved with reduced discomfort or disability glare.
A second kind of glare is veiling glare, which is due to specular reflection from glossy surfaces. The image of the light source overlays the image on the glossy surface reducing contrast and, therefore, visibility. One of the means for reducing veiling glare is to control the light beam from the fixture to eliminate illuminating angles that would produce veiling glare in specified applications. In conventional light fixture designs, the distribution of the light is usually controlled by reflector design. For precise directional control of light, specular reflectors are used. (See "The Optical Design of Reflectors" by William B. Elmer, John Wiley & Sons, 1980.) If transmission optics are used, they are generally used to supplement the reflector design or to provide protection of the light fixture from the environment. This addition of transmission optics to light fixtures lowers the efficiency due to losses in the transmission optics and are, therefore, shunned by some designers. (See W. B. Elmer, cited above.) Specular reflector optics can be used to reduce some veiling glare by careful control of the light beam. Baffles are sometimes added to improve or limit the beam. However, they do not reduce the direct disability glare. Diffusing reflectors can lower the disability glare but are much less effective in reducing veiling glare due to the loss of directional control. Another method for reducing disability glare is to place a large area diffusor in front of the light source. This lowers the surface luminance of the light fixture, but also reduces the control of the light direction which can result in veiling a glare. A light fixture with both lowered surface luminance and controlled light beam direction would provide for significant glare reduction in a wide range of applications.